I have a two-wire thermostat and an old forced air gas furnace in my house. When you open up the cabinet, inside you find a Dayton 2E228 Gas Valve and it is wired to an external 24VAC Transformer apparently "in series" with the thermostat. Here's a schematic of what I traced out:
I got an Ecobee3, and discovered to my disappointment it requires a third wire in the thermostat cable for a 24VAC transformer common (C) to power it. Following the trail, I went off and bought a Fast-Stat Commonmaker to try and solve the problem. You look at the wiring diagram that they propose in the manual for a system ostensibly like mine with a gas valve, and it doesn't really resemble what I've got. The valve in their example is wired in parallel with the transformer:
I tried to rewire the gas valve + transformer + Commonmaker according to that diagram assuming that the TH terminals correspond to the THERM side of my gas valve, and the TR terminals correspond to the TRANS side of my gas valve, but my gas valve must be different somehow from what the Commonmaker instructions are describing. I did manage to get the Ecobee3 to power up after doing that, but it was not turning my furnace on.
I've put everything back the way it was with my old thermostat so that I don't freeze overnight and it seems to be working. Could anyone offer any advice on how to correctly wire the Commonmaker into my primitive / old HVAC system such that my Ecobee3 thermostat can both power up and control the temperature in my home?